// ඞ
#pragma GCC optimize("Ofast")
//#pragma GCC target("popcnt")
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
#ifdef LOCAL
#include "debug.h"
#define dbg(...) debug_out(splitter(#__VA_ARGS__), 0, __LINE__, __VA_ARGS__)
#else
#define dbg(...)
#endif
//#define int long long
#define itn int
#define ALL(v) (v).begin(), (v).end()
#define mem(a, x) memset(a , x , sizeof(a))
#define f first
#define s second
#define mb make_pair
#define pb push_back
#define popCnt __builtin_popcountll
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<vector<int>> vvi;
typedef pair <int, int> pii;
typedef vector<pair <int, int>> vpii;
typedef vector<vector<char>> vvc;
const int mod = 1e9 + 7;
const int oo = 0x5f5f5f5f;
const long double PI = acos(-1.0L);
int ceiledLog2 (int x){return __lg(x) + (__builtin_popcount(x) != 1);}
ll toLL (int first, int second, int mx){return (1LL*first*mx) + second;}
template <class T, class U> T GCD (T a, U b) {return (!b ? a : GCD(b, a%b));}
template <class T, class U> T LCM (T a, U b) {return ((a/GCD(a, b)) * b);}
template <class T> bool isSquare (T n) {T sq = sqrt(n); return (sq*sq)==n;}
template <typename T> T Unique(T x){sort(ALL(x));x.resize(distance(x.begin(),unique(ALL(x))));return x;}
template <typename T> using oset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
//bool sortBySecond (pii &a, pii &b) {return a.second < b.second;} //asc
int ys[] = {-1, -1, 0, 1, 1, 1, 0, -1}; //edges [0, 2, 4, 6]
int xs[] = {0, 1, 1, 1, 0, -1, -1, -1};
//-----------------------------------------------------------------------------//
//const int N = ?e5 + 5;
int n,k;
vector<vpii> g;
int ans=2e9;
struct B_CH_SACK {
int n, timer = 0;
vector<int> lev,sz, b_ch;
vector<ll>to;
vector<int> order, tin, tout;
map<ll, int> f;
B_CH_SACK(int _n = 0) {
n = _n;
if (n) {
sz.resize(n, 1);
to.resize(n);
lev.resize(n);
b_ch.resize(n, -1);
tin.resize(n);
tout.resize(n);
dfs(0, -1);
solve(0, -1, false);
}
}
void dfs(int u, int p, ll t=0, int d=0) {
tin[u] = timer++;
order.push_back(u);
to[u]=t;
lev[u]=d;
int mx = 0, idx = -1;
for (auto &[v,c] : g[u]) {
if (v == p) continue;
dfs(v, u, t+c,d+1);
sz[u] += sz[v];
if (sz[v] > mx) {
mx = sz[v];
idx = v;
}
}
b_ch[u] = idx;
tout[u] = timer-1;
}
void solve(int u, int p, bool keep) {
for (auto &[v,c] : g[u]) {
if (v == p || v == b_ch[u]) continue;
solve(v, u, false);
}
if (b_ch[u] != -1) {
solve(b_ch[u], u, true);
}
f[to[u]]=lev[u];
for (auto &[v,c] : g[u]) {
if (v == p || v == b_ch[u]) continue;
for (int i = tin[v]; i <= tout[v]; i++) {
int x = order[i];
ll d=to[x]-to[u];
if (d>k) continue;
ll dif=k-d;
dif+=to[u];
if (f.count(dif)){
ans=min(ans, f[dif]-lev[u] + lev[x]-lev[u]);
}
}
for (int i = tin[v]; i <= tout[v]; i++) {
int x = order[i];
if (f.count(to[x]))
f[to[x]]=min(f[to[x]],lev[x]);
else
f[to[x]]=lev[x];
}
}
ll need=to[u]+k;
if (f.count(need)){
ans=min(ans, f[need]-lev[u]);
}
if (!keep) {
f.clear();
}
}
} sack;
int best_path(int N, int K, int h[][2], int l[]){
n=N;
k=K;
g=vector<vpii>(n);
for (int i = 0; i < n-1; ++i) {
g[h[i][0]].pb({h[i][1], l[i]});
g[h[i][1]].pb({h[i][0], l[i]});
}
sack=B_CH_SACK(n);
if (ans > 1e8)
return -1;
return ans;
}
